Optical Low-coherence Interferometry Research Articles

Strain Sensing Comparison Between Single and Multimode Fibers using Optical Low Coherence Interferometry

Optical low coherence interferometry is one of the accurate optical sensing technologies and widely utilized in various physical sensing properties. The system principle is to characterize the relative interferogram movement distance caused by the various strain on a sensing arm. An interferometric strain sensor from two-stage Mach-Zehnder interferometer was demonstrated for double sensitivity improvement. The strain performance comparison between single and multimode fibers will be analyzed for fiber sensing applications. The stepper motor was set up with a movement distance of 20 nm in every step and the velocity could achieve 10000 step/s. The fiber strain was characterized as 22.22 μe on a 9-cm length. The experimental results demonstrated the multimode fiber sensitivity is higher than single mode fiber. Repeatability of both single and multimode are uncertain. The interferogram movement distance from the multimode fiber was higher than a single mode and demonstrates higher sensitivity

Complete Dispersion Characterization of Few Mode Fibers by OLCI Technique

Few-mode optical fibers (FMFs) are useful for many applications such as space-division-multiplexing (SDM), high laser power generation and transport, dispersion compensation, etc. The emergence of SDM induces considerable requirements in terms of FMF characterization (chromatic dispersion, birefringence, modal content, bending losses). All LP modes of an FMF can be simultaneously characterized using phase-sensitive optical low-coherence interferometry. The differential modal group delay and absolute chromatic dispersion values of each mode are retrieved from a single measurement without spatial mode transformers.

Two-dimensional high-speed and long-range tomography and profilometry using liquid-crystal Fabry-Perot resonator.

A two-dimensional high-speed, long-range tomography and profilometry based on a low-coherence optical interferometry has been developed. A liquid-crystal Fabry-Perot resonator is fabricated to be a low-coherence optical frequency comb generator for expanding the measurement depth of the tomography and profilometry. The line-shape interference fringes with the individual fringe orders are obtained by a CCD camera in real time. The relative optical length, corresponding to the sample depth information, can be derived from the positions of the interference fringes on the CCD camera and their corresponding fringe orders. The fringe orders can be rapidly calculated using the effectiveness of the changeable extraordinary refractive index of the liquid-crystal material of the resonator. The finesse of the liquid-crystal resonator is approximate 9, giving an expansion of the measurement range of up to 9-fold (∼8 mm depth) with a resolution of profilometry and tomography of 3.7μm and 11μm, respectively.

Involvement of GABA transporters in atropine-treated myopic retina as revealed by iTRAQ quantitative proteomics.

Atropine, a muscarinic antagonist, is known to inhibit myopia progression in several animal models and humans. However, the mode of action is not established yet. In this study, we compared quantitative iTRAQ proteomic analysis in the retinas collected from control and lens-induced myopic (LIM) mouse eyes treated with atropine. The myopic group received a (−15D) spectacle lens over the right eye on postnatal day 10 with or without atropine eye drops starting on postnatal day 24. Axial length was measured by optical low coherence interferometry (OLCI), AC-Master, and refraction was measured by automated infrared photorefractor at postnatal 24, 38, and 52 days. Retinal tissue samples were pooled from six eyes for each group. The experiments were repeated twice, and technical replicates were also performed for liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis. MetaCore was used to perform protein profiling for pathway analysis. We identified a total of 3882 unique proteins with <1% FDR by analyzing the samples in replicates for two independent experiments. This is the largest number of mouse retina proteome reported to date. Thirty proteins were found to be up-regulated (ratio for myopia/control > global mean ratio + 1 standard deviation), and 28 proteins were down-regulated (ratio for myopia/control < global mean ratio - 1 standard deviation) in myopic eyes as compared with control retinas. Pathway analysis using MetaCore revealed regulation of γ-aminobutyric acid (GABA) levels in the myopic eyes. Detailed analysis of the quantitative proteomics data showed that the levels of GABA transporter 1 (GAT-1) were elevated in myopic retina and significantly reduced after atropine treatment. These results were further validated with immunohistochemistry and Western blot analysis. In conclusion, this study provides a comprehensive quantitative proteomic analysis of atropine-treated mouse retina and suggests the involvement of GABAergic signaling in the antimyopic effects of atropine in mouse eyes. The GABAergic transmission in the neural retina plays a pivotal role in the maintenance of axial eye growth in mammals.

Highly efficient higher-order modes filtering into aperiodic very large mode area fibers for single-mode propagation.

We report here on the first experimental demonstration, to the best of our knowledge, of a new generation of very large mode area (VLMA) fibers intended to strengthen single-mode propagation. The originality of this work relies on an aperiodicity of the inner cladding microstructuration exacerbating the spatial rejection of higher-order-modes (HOMs) while preserving a significant confinement of the fundamental mode. The single-mode behavior was demonstrated using an optical low-coherence interferometry measurement based on the group-velocity dispersion. As suggested through a preliminary numerical approach, this outstanding characteristic/behavior is evidenced over a large spectral range spanning from 1 to 2μm for a core diameter of 60μm. Core scalability was also investigated.

Biosensing Using Microring Resonator Interferograms

Optical low-coherence interferometry (OLCI) takes advantage of the variation in refractive index in silicon-wire microring resonator (MRR) effective lengths to perform glucose biosensing using MRR interferograms. The MRR quality factor (Q), proportional to the effective length, could be improved using the silicon-wire propagation loss and coupling ratio from the MRR coupler. Our study showed that multimode interference (MMI) performed well in broad band response, but the splitting ratio drifted to 75/25 due to the stress issue. The glucose sensing sensitivity demonstrated 0.00279 meter per refractive-index-unit (RIU) with a Q factor of ∼30,000 under transverse electric polarization. The 1,310 nm DFB laser was built in the OLCI system as the optical ruler achieving 655 nm characterization accuracy. The lowest sensing limitation was therefore 2 × 10−4 RIU. Moreover, the MRR effective length from the glucose sensitivity could be utilized to experimentally demonstrate the silicon wire effective refractive index with a width of 0.45 μm and height of 0.26 μm.

Polarization-resolved imaging of an ensemble of waveguide modes

We demonstrate polarization-sensitive measurement of the modal content of waveguides by generalizing the classic rotating wave-plate-based polarimeter to wide-field optical low-coherence interferometry. The spatial phases of the modes are retrieved with principal component analysis. By applying this polarization-sensitive cross-correlation (C2) imaging technique to the characterization of a few-mode fiber, we reveal that different modes experience distinct bend-induced birefringence in optical fibers. This polarization-resolved C2 imaging is well suited for analyzing the impact of polarization on wave propagation in high-power fiber lasers as well as in mode-division-multiplexed communications systems.

Simultaneous shape measurement and layers detection by means of low coherence interferometry and optical coherence tomography

In this paper authors show the application of low coherence interferometry and optical coherence tomography with non-Gaussian light source, which are applicable in simultaneous measurement of micromembrane and detection of layers deposited on silicon wafer. The exemplary measurement results obtained with laboratory setup are presented. Full Text: PDF References D. Huang, et al. "Optical coherence tomography", Science, Vol. 254, 1178 (1991). CrossRef A. Dubois, L. Vabre, A.C. Boccara and E.l Beaurepaire, "High-Resolution Full-Field Optical Coherence Tomography with a Linnik Microscope", Appl. Opt. Vol. 41, 805 (2002). CrossRef J.W. Goodman, Statistical Optics (John Wiley & Sons 1985). A. Harasaki, J. Schmit and J.C. Wyant, "Offset of Coherent Envelope Position Due to Phase Change on Reflection", Appl. Opt. Vol. 40, 2101 (2001). CrossRef G. Kieran, J. Larkin, "Efficient nonlinear algorithm for envelope detection in white light interferometry", J. Opt. Soc. Am. A, Vol. 13, 832 (1996). CrossRef A. Hirabayashi, H. Ogawa and K. Kitagawa, "Fast Surface Profiler by White-Light Interferometry by use of a New Algorithm Based on Sampling Theory", Appl. Opt. Vol. 41, 4876 (2002). CrossRef J. Plucinski et al., "Optical low-coherence interferometry for selected technical applications", Bulletin of the Polish Academy of Sciences, Vol. 56, 155 (2008). DirectLink A. Pakula, L. Salbut, Fringe 2009, Springer, 358 (2009). S. Chen, A.W. Palmer, "Fringe order identification in optical fibre white-light interferometry using centroid algorithm method", Electronics Lett., Vol. 28, 553, (1992). CrossRef A. Sabac, C. Gorecki and M. Jozwkik, "Design, testing, and calibration of an integrated Mach-Zehnder-based optical read-out architecture for MEMS characterization", Proc SPIE, VOL. 5458, 141 (2004). DirectLink

Ultrasonography and Optical Low-Coherence Interferometry Compared in the Chicken Eye

To compare ocular biometry [anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL)] using A-scan ultrasonography and optical low-coherence interferometry (OLCI) in the chicken eye. Two-week-old chicks (n = 42) were measured. Bland-Altman plots and repeatability and correlation analyses were calculated for both methods. There was a high correlation between both methods for ACD (r = 0.6144, p < 0.0001), VCD (r = 0.9595, p < 0.0001), and AL (r = 0.9290, p < 0.0001) but not for LT (r = 0.1604, p = 0.144). Measurements by OLCI were more consistent (smaller coefficients of variation and higher intraclass correlation). Bland-Altman plots showed that ultrasound provided larger values for LT, VCD, and AL but not for ACD [differences between ultrasound and OLCI (mean ± SD): ACD = -0.11 ± 0.12 mm; LT = 0.10 ± 0.09 mm; VCD = 0.25 ± 0.08 mm; AL = 0.50 ± 0.16 mm]. A high correlation between both techniques was found for three of the four parameters (ACD, VCD, and AL). However, as the absolute values were different, both techniques cannot replace each other mainly because (1) one is non-contact and the other contact and can induce a minor indentation of the cornea and (2) each device uses different types of waves that cross the ocular interfaces differently. While consistency and repeatability were better by OLCI, a disadvantage is that, different from humans, it can only be used in anesthetized chicks.

Analysis of micromachined Fabry-Pérot cavities using phase-sensitive optical low coherence interferometry: Insight on dimensional measurements of dielectric layers

Herein, we highlight a behavior underlying the physics of Fabry-Pérot micro-cavities with distributed reflectors as there is a need to discriminate between effective and physical cavity lengths. Hence, Phase-Sensitive Optical Low Coherence Interferometry has been implemented to characterize micro-cavities with planar or curved reflectors. Beside the retrieved physical length, we obtain valuable information about the reflector thickness and number of layers. The accuracy of the technique has been estimated. Results suggest that this technique might be suitable to retrieve dimensional characteristics of any device constructed from multiple dielectric layers, whose thickness ranges from 2 micrometers up to hundreds of micrometers.

ZrO2 thin-film-based sapphire fiber temperature sensor

A submicrometer-thick zirconium dioxide film was deposited on the tip of a polished C-plane sapphire fiber to fabricate a temperature sensor that can work to an extended temperature range. Zirconium dioxide was selected as the thin film material to fabricate the temperature sensor because it has relatively close thermal expansion to that of sapphire, but more importantly it does not react appreciably with sapphire up to 1800 °C. In order to study the properties of the deposited thin film, ZrO2 was also deposited on C-plane sapphire substrates and characterized by x-ray diffraction for phase analysis as well as by atomic force microscopy for analysis of surface morphology. Using low-coherence optical interferometry, the fabricated thin-film-based sapphire fiber sensor was tested in the lab up to 1200 °C and calibrated from 200° to 1000 °C. The temperature resolution is determined to be 5.8 °C when using an Ocean Optics USB4000 spectrometer to detect the reflection spectra from the ZrO2 thin-film temperature sensor.

Fabrication of a Miniaturized Thin-Film Temperature Sensor on a Sapphire Fiber Tip

We report a miniature thin-film-based high-temperature sensor prototype with potential for batch fabrication. A thin Tantalum Pentoxide film was deposited on the tip of a polished sapphire fiber using electron-beam evaporation. Using low-coherence optical interferometry, the film was tested as a temperature sensor from 200°C to 1000°C, and its resolution was measured to be 1.4°C. In addition to its potential for low-cost batch production, the sensor's ultra-miniature size of only 75 μm makes it ideal for embedded sensing applications in harsh environments.

The Pathologic Effect of a Novel Neomorphic Fgf9Y162C Allele Is Restricted to Decreased Vision and Retarded Lens Growth

Fibroblast growth factor (Fgf) signalling plays a crucial role in many developmental processes. Among the Fgf pathway ligands, Fgf9 (UniProt: P54130) has been demonstrated to participate in maturation of various organs and tissues including skeleton, testes, lung, heart, and eye. Here we establish a novel Fgf9 allele, discovered in a dominant N-ethyl-N-nitrosourea (ENU) screen for eye-size abnormalities using the optical low coherence interferometry technique. The underlying mouse mutant line Aca12 was originally identified because of its significantly reduced lens thickness. Linkage studies located Aca12 to chromosome 14 within a 3.6 Mb spanning interval containing the positional candidate genes Fgf9 (MGI: 104723), Gja3 (MGI: 95714), and Ift88 (MGI: 98715). While no sequence differences were found in Gja3 and Ift88, we identified an A→G missense mutation at cDNA position 770 of the Fgf9 gene leading to an Y162C amino acid exchange. In contrast to previously described Fgf9 mutants, Fgf9Y162C carriers were fully viable and did not reveal reduced body-size, male-to-female sexual reversal or skeletal malformations. The histological analysis of the retina as well as its basic functional characterization by electroretinography (ERG) did not show any abnormality. However, the analysis of head-tracking response of the Fgf9Y162C mutants in a virtual drum indicated a gene-dosage dependent vision loss of almost 50%. The smaller lenses in Fgf9Y162C suggested a role of Fgf9 during lens development. Histological investigations showed that lens growth retardation starts during embryogenesis and continues after birth. Young Fgf9Y162C lenses remained transparent but developed age-related cataracts. Taken together, Fgf9Y162C is a novel neomorphic allele that initiates microphakia and reduced vision without effects on organs and tissues outside the eye. Our data point to a role of Fgf9 signalling in primary and secondary lens fiber cell growth. The results underline the importance of allelic series to fully understand multiple functions of a gene.

Simultaneous Measurements of Refractive Index and Thickness by Spectral-Domain Low Coherence Interferometry Having Dual Sample Probes

We propose and demonstrate the novel method that enables simultaneous measurements of physical thickness and refractive group index without any prior knowledge on samples. The system is based on the spectral-domain optical low coherence interferometry with two sample probes facing each other. Owing to both side measurements schemes, thickness and group refractive index could be measured with not only transparent but also highly absorptive samples. The average errors were ~0.06% in both the physical thickness and the group refractive index measurements.

Interfaces detection after corneal refractive surgery by low coherence optical interferometry.

The detection of refractive corneal surgery by LASIK, during the storage of corneas in Eye Banks will become a challenge when the numerous operated patients will arrive at the age of cornea donation. The subtle changes of corneal structure and refraction are highly suspected to negatively influence clinical results in recipients of such corneas. In order to detect LASIK cornea interfaces we developed a low coherence interferometry technique using a broadband continuum source. Real time signal recording, without moving any optical elements and without need of a Fourier Transform operation, combined with good measurement resolution is the main asset of this interferometer. The associated numerical processing is based on a method initially used in astronomy and offers an optimal correlation signal without the necessity to image the whole cornea that is time consuming. The detection of corneal interfaces - both outer and inner surface and the buried interface corresponding to the surgical wound – is then achieved directly by the innovative combination of interferometry and this original numerical process.

Non-invasive optical interferometry for the assessment of biofilm growth in the middle ear.

Otitis media (OM) is the most common illness in children in the United States. Three-fourths of children under the age of three have OM at least once. Children with chronic OM, including OM with effusion and recurrent OM, will often have conductive hearing loss and communication difficulties, and need surgical treatment. Recent clinical studies provide evidence that almost all chronic OM cases are accompanied by a bacterial biofilm behind the tympanic membrane (eardrum) and within the middle ear. Biofilms are typically very thin, and cannot be recognized using a regular otoscope. Here we demonstrate how optical low coherence interferometry (LCI) noninvasively depth-ranges into the middle ear to detect and quantify biofilm microstructure. A portable diagnostic system integrating LCI with a standard video otoscope was constructed and used to detect and quantify the presence of biofilms in a newly-developed pre-clinical animal model for this condition. Using a novel classification algorithm for acquired LCI data, the system identified the presence of a biofilm with 86% sensitivity and 90% specificity, compared to histological findings. This new information on the presence of a biofilm, its structure, and its response to antibiotic treatment, will not only provide better understanding of fundamental principles that govern biofilm formation, growth, and eradication, but may also provide much needed clinical data to direct and monitor protocols for the successful management of otitis media.

Active feedback wide-field optical low-coherence interferometry for ultrahigh-speed three-dimensional morphometry

A novel optical interferometric scheme for ultrahigh-speed three-dimensional morphometry is proposed. The system is based on wide-field optical coherence tomography (WF-OCT) but with optically chopped illumination. The chopping frequency is feedback-controlled to be always matched with the Doppler frequency of the OCT interferometer, which provides an efficient page-wide demodulation suitable for ultrahigh-speed volumetric imaging. To compensate the unwanted variation in the OCT Doppler frequency of the system, the illumination frequency is phase-locked with an auxiliary laser interferometer which shares the reference arm with the OCT interferometer. The two-dimensional (2D) interference signals projected on the 2D array pixels of a 200 Hz CCD are accumulated during one imaging frame of the CCD. Then, each pixel of the CCD demodulates the OCT signal automatically. Owing to the proposed active frequency-locked illumination scheme, the demodulation does not depend on the variation in the axial scanning speed. Volumetric topograms or/and tomograms of several samples were achieved and rendered with a sensitivity of 58 dB at an axial scan speed of 0.805 mm s−1.

A rapid method of measuring dispersion in low coherence interferometry and optical coherence tomography systems

A method of using multiple spectral channels to measure dispersion mismatch in optical coherence tomography (OCT) and low coherence interferometry systems is presented. The method is tested on a time domain OCT system in comparison to the measurement of the auto-correlation profile. The method is quicker to implement and is more sensitive than the measurement of the auto-correlation profile.

Microbending behavior of large-effective-area Bragg fibers

We use a phase-sensitive optical low-coherence interferometry technique and camera imaging to identify microbend-induced mode couplings in Bragg fibers. Results show the importance of the quality of fabrication of Bragg fibers on their modal content when they are subject to microbends. Design strategies to improve the microbending robustness are identified.

Polarization- and Phase-Sensitive Low-Coherence Interferometry Setup for the Characterization of Integrated Optical Components

A novel phase-sensitive and polarization-sensitive scheme to implement an optical low-coherence interferometry (OLCI) system is presented. With respect to conventional phase-sensitive OLCI, in our system the interference fringes of the coherent light used to recover phase information are conveniently detected by the same photodetector acquiring the low-coherence signal. This strategy guarantees the intrinsic synchronization of the two signals at any acquisition speed, makes measurements more robust against long-term fluctuations in the experimental setup, and reduces the measurement time without affecting phase accuracy. The residual phase error after the phase recovery procedure is less than 0.01 rad, to the authors' knowledge one of the best results reported so far for OLCI measurements. Polarization sensitivity is achieved in the same setup by means of polarization selective retarders (PSRs) employed to couple light into and out of the device under test. This scheme enables to retrieve the time and frequency domain response of an optical device for both the polarization states from a single data acquisition. The presented technique is extremely versatile; it can be implemented by using either fiber or free space optics and applied to the characterization of generic optical devices. Its effectiveness is demonstrated by reporting the measurement of the amplitude and phase response of integrated optical devices based on ring resonators.